Conventional granules used for bone regenerative filler have solid spherical bodies. One drawback of the solid spherical bodies is low population of cell attachment and proliferation as well as a higher fraction of surgical site was occupied by material than core-centered granule, less space for cell ultimately bone regeneration. It has been unexpectedly found that granules having a generally tubular structure with at least one core defined in the body facilitates cell migration and/or proliferation rate.